1. Field of the Invention
The present invention relates generally to an internal combustion engine for use in marine applications.
2. Description of the Related Art
There exist three main types of engine/propulsion unit arrangements to power boats. They are outboards, inboards, and stern drives.
Outboards, as the name suggests, are located outside of the boat. Outboards have the engine, gear case, and propeller mounted as a complete unit to the transom of the boat. The engine has a vertically oriented driveshaft. Steering is achieved by swiveling the unit to direct the thrust of the propeller.
Inboards have the engine located inside the hull forward of the boat's transom. The engine turns a driveshaft which extends through the hull to a propeller or a jet pump. Where a propeller is used, steering is achieved by using rudders. Where a jet pump is used, steering is achieved by using a nozzle which directs the thrust generated by the pump.
Stem drives have the engine 1 located inside the hull 2 in a manner similar to inboards as seen in FIG. 1. The engine 1 turns a driveshaft (not shown) which is connected through the transom 3 to the drive unit 4. The drive unit 4 is equipped with a propeller 5. The drive unit 4 resembles the lower unit of an outboard. Steering is achieved by swiveling the drive unit 4 to direct the thrust of the propeller 5. Since stem drives combine some of the features of both inboards and outboards, they are also known as inboard/outboards (I/O).
Most stern drives and inboards use four-stroke or diesel automotive engines adapted for marine use (by improving their resistance to corrosion for example), as this represents a simpler, and less expensive (both in terms of time and money) approach than designing an engine specifically for marine uses. Although adequate, since such engines were not specifically designed to be used in a boat, they do not address all the needs of such an application.
When engineers design engines for automotive applications, they are concerned with the constraints resulting from placing the engine inside a car not a boat. One of the design constraints is the height inside which the engine has to fit. This height in a car is greater than a height between a deck floor and a hull of a boat, and as a result engines designed for automotive application are too high to fit between the deck floor and the hull of a boat. Another design constraint is that an engine designed for automotive applications needs to drive wheels located below the engine. In boats such as stern drives, the engine needs to drive a driveshaft located above the bottom of the hull on which the engine sits, as explained in greater detail below. Also, once an engine is installed in a car, the engine and it's components can be accessed relatively easily from above the engine (by opening the hood) and from below the engine (by getting under the car). Once an engine is installed in a boat, it can only be accessed from above since, as it would be understood, the engine cannot be accessed from under the hull, and therefore components located under an automotive engine are very difficult to access for maintenance or replacement when such an engine is placed in a boat. Since the above mentioned constraints for designing an engine for an automotive application conflict what would be necessary for a boat, the decision to use automotive engines in boats has forced boat manufacturers to compromise on the design of their boats.
As seen in FIG. 1, the drive unit 4 needs to be located a certain distance above the bottom of the hull 2 in order to minimize drag and maximize propulsion efficiency, which means that the driveshaft that couples the drive unit 4 to the engine 1 is located relatively high above the bottom of the hull 2. In automotive engines, as in the engine 1, the power take-off assembly is coaxial with the crankshaft located in the crankcase near the bottom of the engine 1. Therefore, in order to couple the power take-off assembly to the driveshaft of the drive unit 4, the engine 1 needs to be mounted high above the bottom of the hull 2. As can be seen in FIG. 1, this combined with the height of automotive engines results in the engine extending well above the deck floor 9 of a boat 6.
FIG. 2 shows the boat 6 equipped with a stern drive. The engine 1 is located inside the boat 6 near the transom. The drive unit 4 is attached to the transom. The drive unit 4 and propeller are located under a swim platform 7 from which people can reboard the boat 6 from the water. For the reasons mentioned above, an openable engine cover 8 in the form of a large box, which extends above the deck floor 9 and the seats, has to be accommodated in the boat 6. As can be seen in FIG. 2, the engine cover 8 takes up a substantial portion of the passenger area. Boat manufacturers have come up with some creative ways to integrate this engine cover 8 to the design of their boats by padding it to allow people to rest on it or by adding cup holders. In reality, the engine cover 8 only occupies valuable room inside the passenger area which boat designer could make better use of if this constraint did not exist. Similar compromises in the design of boats equipped with an inboard have to be made.
Therefore, there exists a need for an engine designed specifically for use in marine applications and more specifically stern drives and inboards.